What is warfarin?Warfarin is an anticoagulant medication that is used to slow down the blood-clotting process. Blood clots may cause vein blockages, heart attack, and stroke. Anticoagulants can prevent blood clots. Brand names for warfarin are Warfant, Jantoven, Coumadin, Lawarin, Marevan, and WaranThere are two main types of blood thinners. Anticoagulants, such as heparin or warfarin (also called Coumadin), work on chemical reactions in your body to lengthen the time it takes to form a blood clot. Antiplatelet drugs, such as aspirin, prevent blood cells called platelets from clumping together to form a clot.